This invention is generally directed to liquid developer compositions containing resin particles, charge adjuvants, optional pigments, and charge directors. More specifically, the present invention relates to liquid developers comprised of a suitable carrier liquid and poyalkylene particles, such as polybutene, polypentene, polypentadecene, and the like, and which developers are suitable for imaging processes including those processes that involve the transfer of developed images from one substrate to another by a process referred to as transfix. In particular, copolymers and terpolymers of 1-butene, 1-pentene, and undecylenic acid were found to possess excellent release characteristics and transfix well from VITON B50.RTM. and VITON GF.RTM. intermediates which represents a stress situation for transfix. Resins for liquid development can require a number of very specific attributes, including for example processable into particles with the desired melting properties, usually between about 60.degree. and about 120.degree. C.; be hydrocarbon swellable or soluble at elevated temperatures but insoluble at temperatures less than about 60.degree. C.; plasticizable with hydrocarbons developable by electrostatic or other imaging processes; releasable from low surface energy elastomers; adherent to paper and plastic films; and optically clear, and mechanically robust. These and other needs are achievable with the liquid toners of the present invent on in embodiments. Also, liquid developers with the polyalkyene resins of the present invention possess superior release and transfer characteristics from, for example, VITON.RTM. intermediates to SENECA IMAGE SERIES LX.TM. and coated papers like KROME KOTE.TM. materials, as compared to other known resins such as NUCREL 599.RTM. selected for liquid developers. With respect to release and transfix, the polyalkylene resins are comparable with or superior to the amine and ester modified NUCREL 599.RTM. resins illustrated in copending patent application Ser. No. 185,343 (D/93428), the disclosure of which is totally incorporated herein by reference. The polyalkylene resins selected for the developers of the present invention possess unique release properties which allow efficient transfix from VITON.RTM. intermediates. Moreover, in embodiments the polyalkylene resin structure can be modified to control the triboelectrical characteristics and melting properties of the developer particles.
The images obtained with developers comprised of the polyalkylene resin particles of the present invention can be developed onto a photorecepter and, subsequently, can be transferred to an intermediate substrates for optional image conditioning before the image is again transferred and permanently adhered to or fixed to the final image receiver, such as paper or plastic film, using heat and pressure means such as rollers. The intermediate substrate is typically comprised of a informable elastomer, such as VITON.RTM., silicone, fluorosilicone, polyphosphazene, fluoropolymer, or a related material with low surface energy to facilitate release. Alternatively, the liquid images can be applied directly to a low surface energy intermediate by known printing methods, silk screening techniques, and the like prior to optional image conditioning, subsequently transferring from the intermediate, and subsequently fixing to the final image receiver which is usually paper. Image conditioning of developed images entails, for example, the heat treatment and blotting of the developed liquid images on an intermediate to form high ink solids images, for example, between 1 and about 100 percent solids of the nonliquid, dry weight of the inks.
The liquid images formed with the developers of the present invention enable improved release from intermediates, and effective transfer and transfix of developed images to the image receiver with improved copy quality. Copy quality improves primarily as a result of the optically clear polyalkylene resins, small particle size developers, low image pile height, and low fixing temperatures which enable image permanence and reduced paper curl.
When electrostatic development is selected for the preparation of images, additional characteristics can include resin particles with appropriate charging properties to permit high resolution images which can be electrostatically transferred to the appropriate intermediate. NUCREL.RTM. resins which are comprised of ethylene-methacrylic acid copolymers have traditionally been used in liquid developers. These resins have excellent triboelectrical properties and acceptable fix, or permanence, and acceptable image quality in most instances. However, the adhesion of NUCREL.RTM. particles to intermediates can render these resins unsatisfactory in transfix processes, that is, for example, for release from intermediates and subsequent transfer to paper. The resins of the present invention enable, for example, the facilitation of the release of images from intermediate substrates without adversely affecting image permanence and image quality.
With the polyalkylene resins as illustrated herein, there are enabled liquid and dry developers with small particle sizes, for example, particles with average volume diameters of between 0.2 and 10 microns, which resins can be obtained by conventional shot mill attrition within about 6 hours; and excellent and improved toner release from, for example, intermediate substrates, and wherein the resulting developed images can be transfixed to substrates such as paper. The developers of the present invention can be selected for a number of known imaging systems, such as xerographic imaging and printing processes, wherein latent images are rendered visible with the liquid developer illustrated herein. The image quality, solid area coverage and resolution for developed images usually require, for example, sufficient toner particle electrophoretic mobility. The mobility for effective image development is primarily dependent on the imaging system used, and this electrophoretic mobility is directly proportional to the charge on the toner particles and inversely proportional to the viscosity of the liquid developer fluid. For example, a 10 to 30 percent change in fluid viscosity caused for instance by a 5.degree. to 15.degree. C. decrease in temperature could result in a decrease in image quality, poor, or unacceptable image development and undesirable background development, for example, because of a 5 percent to 23 percent decrease in electrophoretic mobility. Insufficient particle charge can also result in poor, or no transfer of the toner to paper or other substrates. Poor transfer, for example, can result in poor solid area coverage if insufficient toner is transferred to the final substrate and can also result in image defects such as smearing and hollowed fine features. To overcome or minimize such problems, the liquid toners of the present invention were arrived at after substantial efforts, and which toners result in, for example, sufficient particle charge, generally corresponding to an ESA mobility greater than 1.5 E-10 m.sup.2 /Vs for excellent transfer, maintaining their mobility within the desired range of the particular imaging system employed, and the developer conductivity thereof is usually maintained between 5 and 20 ps/centimeter. Other advantages associated with the developers of present invention include the use of certain polyalkylene resins particles for satisfactory development and improved transfix.
The polyalkylene resins can be chemically modified with undecylenic acid groups and related derivatives by copolymerization with undecylenic acid, undecylenyl iodide, and the like, and subsequent derivatization to form quaternary ammonium groups to improve the respective negative or positive charging properties of the developer. The concentration of functional groups attached to the alkylene copolymers range from between about 0.1 and about 25 weight percent and preferably from between about 1 and 15 weight percent.
Specific alkylene copolymers of the present invention include the following: polybutene with between 0.5 and 25 weight percent of undecylenic acid groups, polybutene with between 15 and 20 weight percent of pentene and with between 0.5 and 25 weight percent of undecylenic acid groups, polypentene with between 0.5 and 25 weight percent of undecylenic acid groups, and the like. Similar compounds with quarternary ammonium groups derived from undecylenic acid or undecylenyl iodide can also be used in place of undecylenic acid to control the charging properties of the toners.
A latent electrostatic image can be developed with toner particles dispersed in an insulating nonpolar liquid. The dispersed materials are known as liquid toners or liquid developers. A latent electrostatic image may be generated by providing a photoconductive layer with a uniform electrostatic charge and subsequently discharging the electrostatic charge by exposing it to a modulated beam of radiant energy. Other methods are also known for forming latent electrostatic images such as, for example, providing a carrier with a dielectric surface and transferring a preformed electrostatic charge to the surface. After the latent image has been formed, the image is developed by colored toner particles dispersed in a nonpolar liquid. The image may then be transferred to a receiver sheet. Also known are ionographic imaging systems.
Typical liquid developers can comprise a thermoplastic resin and a dispersant nonpolar liquid. Generally, a suitable colorant, such as a dye or pigment, is also present in the developer. The colored toner particles are dispersed in a nonpolar liquid which generally has a high volume resistivity in excess of 10.sup.9 ohm-centimeters, a low dielectric constant, for example below 3.0, and a high vapor pressure. Generally, the toner particles are less than 30 .mu.m (microns) and, for example, from about 5 to about 25 microns average by area size as measured with the Matvern 3600E particle sizer or from about 0.2 to about 10 microns (area average diameter) as measured with the Horiba CAPA 500 or 700 centrifugal particle size analyzer.
Since the formation of proper electrostatic images depends on the difference of the charge between the toner particles in the liquid developer and the latent electrostatic image to be developed, it is desirable to add a charge director compound and optional charge adjuvants (charge control agent) ,which increase the magnitude of the charge, such as polyhydroxy compounds, amino alcohols, polybutylene succinimide compounds, aromatic hydrocarbons, metallic soaps, and the like, to the liquid developer comprising the thermoplastic resin, the nonpolar liquid and the colorant. A charge director can be of importance in controlling the charging properties of the toner to enable excellent quality images. Also, the hydrocarbon side chains of the polyalkylene resin particles selected enables, in of themselves, improved image toner release from a number of substrates.
In U.S. Pat. No. 5,035,972, the disclosure of which is totally incorporated herein by reference, there are illustrated liquid developers with unmodified resins and quaternized ammonium AB diblock copolymer charge directors, and wherein the nitrogen in the ionic A block is quaternized with an alkylating agent.
U.S. Pat. No. 5,019,477, the disclosure of which is totally incorporated herein by reference, illustrates a liquid electrostatic developer comprising a nonpolar liquid, unmodified thermoplastic resin particles, and a charge director. The ionic or zwitterionic charge directors may include both negative charge directors such as lecithin, oil-soluble petroleum sulfonate and alkyl succinimide, and positive charge directors such as cobalt and iron naphthenates. The thermoplastic resin particles can comprise a mixture of (1) a polyethylene homopolymer or a copolymer of (i) polyethylene and (ii) acrylic acid, methacrylic acid or alkyl esters thereof, wherein (ii) comprises 0.1 to 20 weight percent of the copolymer; and (2) a random copolymer of (iii) selected from the group consisting of vinyl toluene and styrene, and (iv) selected from the group consisting of butadiene and acrylate. As the copolymer of polyethylene and methacrylic acid or methacrylic acid alkyl esters, NUCREL.RTM. may be selected. Disadvantages associated with the aforementioned liquid developers are as indicated herein and include, for example, poor toner release, in many instances between 0 and 30 percent image transfer from substrates, and difficulty in grinding particles to dimensions of less than 2 microns, and preferably from submicron to about 2 microns volume average diameter, as determined using the Horiba CAPA 500 or 700 particle size analyzer.
U.S. Pat. No. 5,030,535 discloses liquid developer compositions comprising a liquid vehicle, a charge control additive and toner particles. The toner particles may contain pigment particles and a resin selected from the group consisting of polyolefins, halogenated polyolefins and mixtures thereof. The liquid developers are prepared by first dissolving the polymer resin in a liquid vehicle by heating at temperatures of from about 80.degree. C. to about 120.degree. C., adding pigment to the hot polymer solution and attriting the mixture, and then cooling the mixture so that the polymer becomes insoluble in the liquid vehicle, thus forming an insoluble resin layer around the pigment particles.
Although the developers of the U.S. Pat. No. 5,030,535 can be sufficient for their intended purposes, a number of problems relating to triboelectrical charging and copy quality thereof were encountered when colorants other than carbon black were used. Specifically, developers prepared with many polyolefin resins without functional groups are difficult to charge triboelectrically even in combination with known charge adjuvant compounds when the developer particles are prepared with colorants other than carbon black. Also, carbon black was found to have a substantial effect on the triboelectrical properties and image quality of the poly-1-olefin developers of the '535 patent. Certain long chain poly-1-olefins like poly-1-hexadecene, poly-1-octadecene, and the like of the 5,030,535 patent demonstrate excellent release from VITON.RTM. intermediates; however, the images without carbon black fillers were greasy and prone to smear (like crayons). Poly-1-pentene, poly-1-butene, and poly-1-pentadecene developers prepared in accordance with the 5,030,535 patent were found to have excellent release from VITON.RTM. intermediates and the images were not greasy. However, developer charging remained a problem when colorants other than carbon black were used. Thus, new polyalkylene resins for liquid developers were needed which possessed improved image quality for the production of high resolution color images. The polyalkylene developers of the instant invention offer improved developer charging properties with most colorants in addition to carbon black, and provide improved copy quality without adversely affecting the release of toned images in transfix.
U.S. Pat. No. 4,707,429 discloses, for example, liquid developers with unmodified resins, and an aluminum stearate charge adjuvant. Liquid developers with charge directors are illustrated in U.S. Pat. No. 5,045,425.
U.S. Pat. No. 4,952,477 discloses dry xerographic toner and developer compositions containing semicrystalline polyolefin resins, while U.S. Pat. No. 5,030,535 teaches liquid developer compositions containing polyolefin resins. U.S. Pat. No. 5,166,026 (D/89062) teaches dry toner resins containing eicosene polymers with iodo, quaternary ammonium, amino, and amide functionalities. The disclosures of each of these patents and other patents mentioned herein relating to liquid developers are totally incorporated herein by reference.
In copending patent application Ser. No. 986,316, the disclosure of which is totally incorporated herein by reference, there is illustrated a process for forming images which comprises (a) generating an electrostatic latent image; (b) contacting the latent image with a developer comprising a colorant and a substantial amount of a vehicle with a melting point of at least about 25.degree. C., the developer having a melting point of at least about 25.degree. C., the contact occurring while the developer is maintained at a temperature at or above its melting point, the developer having a viscosity of no more than about 500 centipoise and a resistivity of no less than about 10.sup.8 ohm-cm at the temperature maintained while the developer is in contact with the latent image; and (c) cooling the developed image to a temperature below its melting point subsequent to development.
In U.S. Pat. No. 5,306,591 (D/92570), and U.S. Pat. No. 5,308,731, the disclosures of which are totally incorporated herein by reference, there is illustrated a liquid developer comprised of unmodified thermoplastic resin particles, a charge director, and a charge adjuvant comprised of an imine bisquinone; and a liquid developer comprised of a liquid, unmodified thermoplastic resin particles, a nonpolar liquid soluble charge director, and a charge adjuvant comprised of a metal hydroxycarboxylic acid, respectively. The charge adjuvants and other appropriate components of these patents may be selected for the liquid toners of the present invention.
In copending patent application Ser. No. 065,414, the disclosure of which is totally incorporated herein by reference, there is illustrated a liquid developer comprised of thermoplastic resin particles, and a charge director comprised of an ammonium AB diblock copolymer of the formula ##STR1## wherein X.sup.- is a conjugate base or anion of a strong acid; R is hydrogen or alkyl; R' is alkyl; R" is an alkyl group containing from about 6 to about 20 carbon atoms; and y and x represent the number average degree of polymerization (DP) wherein the ratio of y to x is in the range of from about 10 to 2 to about 100 to 20.
In copending application Ser. No. 185,343, there are illustrated liquid developers with ester, or amide modified resins. Liquid developers prepared with amide and ester modified resins offer improved release compared with NUCREL 599.RTM. control resin. Advantages of the economical alkylene resins over the aforementioned amide and ester modified resins include unique and improved performance, and superior releach characteristics in embodiments.
Illustrated in U.S. Pat. No. 5,409,796, the disclosure of which is totally incorporated herein by reference, is a positively charged liquid developer comprised of thermoplastic resin particles, optional pigment, a charge director, and a charge adjuvant comprised of a polymer of an alkene and unsaturated acid derivative; and wherein the acid derivative contains pendant ammonium groups, and wherein the charge adjuvant is associated with or combined with said resin and said optional pigment; in application Ser. No. 204,012, the disclosure of which is totally incorporated herein by reference, is a negatively charged liquid developer comprised of thermoplastic resin particles, optional pigment, a charge director, and an insoluble charge adjuvant comprised of a copolymer of an alkene and an unsaturated acid derivative, and wherein the acid derivative contains pendant fluoroalkyl or pendant fluoroaryl groups, and wherein the charge adjuvant is associated with or combined with said resin and said optional pigment; and in application Ser. No. 204,016, the disclosure of which is totally incorporated herein by reference, is a liquid developer comprised of thermoplastic resin particles, optional pigment, and a charge director comprised of a mixture of an organic anionic complex phosphate ester and organic aluminum complex, or mixtures thereof of the formulas ##STR2## wherein R.sub.1 is selected from the group consisting of hydrogen and alkyl, and n represents a number.
The disclosures of each of the patents and the copending patent applications recited are totally incorporated herein by reference.